1. Field of the Invention
The present invention generally relates to systems for managing rights of use of digital files. Two types of rights of use can essentially be distinguished. A first so-called number-condition type of rights relates to the possibility of using a digital file a predetermined number of times. A second so-called time-condition type of rights relates to the possibility of using a digital file for a predetermined cumulated time or until a predetermined closing date.
2. Description of the Related Art
Among examples of application of the present invention, the management of rights of use of video files, of music (MP3), radio, or broadcasting files will be mentioned. The rights of use or of exploitation of contents managed by a time-condition system are most often direct rights of use, that is, rights of listening to an audio digital file or of screening a video sequence. Other exploitation rights such as the copying, the transfer, or the printing of digital data are generally managed by systems linked to number conditions rather than to time conditions. It is however not excluded for right management systems to use time conditions (for example, calendar) to set a time period during which the person entitled to the rights is allowed to copy, lend, transfer, or print a digital content.
FIG. 1 very schematically shows in the form of blocks an example of an integrated circuit enabling management of time-condition rights. The circuit comprises a functional block 4 (FUNCT) enabling reading of a memorized music file, for example, downloaded from means not shown. Block 4 is a synchronous block which operates at the rate of a clock signal CK. The frequency of signal CK, from which block 4 especially generates music signals, must be very accurate. For this reason, signal CK is generated by a quartz oscillator 6. In the state of the art, it is impossible to integrate such an oscillator in an integrated circuit, and oscillator 6 is external to circuit 2. A counter 8 (CNT1) clocked by clock signal CK, gives a time measurement. The music file that can be read by block 4 contains, for example, a closing date. Block 4 comprises means not shown to compare the closing date and content CNT of counter 8, and to enable reading of the music file until the content of counter 8 is greater than the closing date.
The time measurement represented by the content of counter 8 is only reliable if circuit 2 remains permanently in operation, and remains clocked by a clock signal CK, the frequency of which does not change. Known means enable verifying that circuit 2 remains in operation and permanently receives a clock signal, to forbid the reading of a music file memorized after a stopping of circuit 2 or of signal CK.
However, since quartz oscillator 6 is external to circuit 2, it remains possible, without stopping signal CK, to reduce its frequency between two uses of circuit 2 to delay, in unauthorized fashion, the time at which the content of counter 8 exceeds the closing date (be it by a calendar testing or by a maximum duration).